The present invention relates to a swash plate type variable displacement compressor.
Japanese Patent Application Publication No. H05-172052 discloses a conventional swash plate type variable displacement compressor (hereinafter simply referred to as compressor). The compressor has a housing that has therein a suction chamber, a discharge chamber, a swash plate chamber, a center bore and a plurality of cylinder bores. The swash plate chamber is in communication with the center bore. A drive shaft is rotatably supported in the housing. The swash plate chamber has therein a swash plate that is mounted on the drive shaft for rotation therewith. A link mechanism is provided between the drive shaft and the swash plate that permits changing of an inclination angle of the swash plate, that is, an angle of the swash plate relative to an imaginary plane extending perpendicularly to the axis of the drive shaft. A piston is reciprocally slidably received in each cylinder bore. Each piston has a pair of shoes that acts as a conversion mechanism, so that the rotation of the swash plate is converted into reciprocating motion of the piston in the cylinder bore with a length of stroke that is determined in accordance with the inclination angle of the swash plate. The compressor further has an actuator that changes the inclination angle of the swash plate and a control mechanism that controls the actuator.
The actuator has a first moving body, a second moving body and a pressure control chamber. The first moving body and the second moving body are slidably mounted on the drive shaft in alignment with each other. The first moving body is disposed in the center bore. A thrust bearing is provided between the first moving body and the second moving body. The swash plate is connected to the second moving body in such a manner that permits the inclination angle of the swash plate to be changed. The pressure control chamber is formed in the center bore by the first moving body. The first moving body and the second moving body are movable by the internal pressure of the pressure control chamber. A coil spring is provided in the pressure control chamber that urges the first moving body in the direction that increases the inclination angle of the swash plate.
In this compressor, the control mechanism allows part of refrigerant in the discharge chamber into the pressure control chamber thereby to increase pressure in the pressure control chamber. The control mechanism introduces a refrigerant into the pressure control chamber. Movement of the first moving body in the center bore in the axial direction of the drive shaft causes the second moving body to move in the same axial direction. Thus, the inclination angle of the swash plate is increased by the movement of the second moving body via the link mechanism. Thus, the discharge volume per rotation of the drive shaft, i.e. the displacement of the compressor, is increased.
When the pressure in the pressure control chamber is decreased by the control mechanism, the first moving body is moved by the reaction force of compressed gas in the direction that decrease the inclination angle of the swash plate against the urging force of the coil spring. The second moving body is also moved in the same direction as the first moving body, thereby reducing the inclination angle of the swash plate via the link mechanism. Thus, the discharge volume per rotation of the drive shaft and hence the displacement of the compressor is reduced.
In the above-descried compressor that changes displacement by the actuator, however, it is desirable that the displacement should be able to be decreased effectively, as well as be increased effectively. For this purpose, an urging member that urges the first and second moving bodies may be employed so as to effectively reduce the displacement of the compressor. If the urging member is small in size, however, the urging force may not be large enough to reduce the displacement effectively. If the urging member is large, on the other hand, it becomes difficult to secure a space that is large enough for installation the urging member in the housing, with the result that the size of the compressor is increased.
The present invention, which is made in light of the problems mentioned above, is directed to offering a swash plate type variable displacement compressor, having an actuator that changes the displacement, that can effectively reduce the displacement while permitting downsizing of the compressor.